Put the syzygy targets behind a 'syzygy_optimize' flag.

chrome/chrome_syzygy.gypi

 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Intended to be included by chrome_syzygy.gyp. A variable 'dll_name' should
 # be set to the base name of the DLL. This is used to generate the build steps
 # for both chrome.dll and chrome_child.dll when in multiple dll mode.
 {
   # Reorder or instrument the initial chrome DLL executable, placing the
   # optimized output and corresponding PDB file into the "syzygy"
   # subdirectory.
   # This target won't build in fastbuild, since there are no PDBs.
   'dependencies': [
     '<(DEPTH)/chrome/chrome.gyp:<(dll_name)_dll',
   ],
   'variables': {
     'dest_dir': '<(PRODUCT_DIR)/syzygy',
   },
   'conditions': [
-    ['syzyasan!=1', {
+    ['syzyasan==0 and syzygy_optimize==1', {
       # Reorder chrome DLL executable.
       # If there's a matching chrome.dll-ordering.json file present in
       # the output directory, chrome.dll will be ordered according to
       # that, otherwise it will be randomized.
       'actions': [
         {
           'action_name': 'Reorder Chrome with Syzygy',
           'inputs': [
             '<(PRODUCT_DIR)/<(dll_name).dll',
             '<(PRODUCT_DIR)/<(dll_name).dll.pdb',
           ],
           'outputs': [
             '<(dest_dir)/<(dll_name).dll',
             '<(dest_dir)/<(dll_name).dll.pdb',
           ],
           'action': [
             'python',
             '<(DEPTH)/chrome/tools/build/win/syzygy_reorder.py',
             '--input_executable', '<(PRODUCT_DIR)/<(dll_name).dll',
             '--input_symbol', '<(PRODUCT_DIR)/<(dll_name).dll.pdb',
             '--destination_dir', '<(dest_dir)',
           ],
         },
       ],
-    }, {
+    }],
+    ['syzyasan==1 and syzygy_optimize==0', {
       # Instrument chrome DLL executable with SyzyAsan.
       'actions': [
         {
           'action_name': 'Instrument Chrome with SyzyAsan',
           'inputs': [
             '<(DEPTH)/chrome/tools/build/win/win-syzyasan-filter.txt',
             '<(PRODUCT_DIR)/<(dll_name).dll',
           ],
           'outputs': [
             '<(dest_dir)/<(dll_name).dll',
@@ skipping 13 matching lines @@
             '--destination_dir', '<(dest_dir)',
           ],
         },
       ],
       'dependencies': [
         'copy_syzyasan_binaries',
       ],
     }],
   ],
 }